One of the central problems in neurobiology is the detailed working out of the ways in which organized systems of neurons accomplish their functions of representing, modifying, and transmitting information and of generating appropriate motor patterns that produce coordinated behaviors. We are studying the organizational principles of neural systems: how the anatomical and physiological properties of the constituent cells combine to comprise a working system. The proposed investigations carry forward previous work in several areas: (1) Mathematical and theoretical studies of principles of interaction in neuronal populations, (2) Development and extension of statistical techniques for the analysis and interpretation of experimentally derived neuroelectric data, including their implementation on digital computers. (3) Development and improvement of digital-computer models for simulating specific neural networks of small to medium size (up to a few hundred components), and their application to well-known invertebrate systems such as crustacean and molluscan ganglia. (4) Simulation on the computer of large-scale neuronal systems, such as the frog cerebellum and the vertebrate retina. (5) Simulating the evolution of branching configurations of nerve axons and dendrites in tissue culture and during development.